ex won't treat for threadworms

Stupid fecker. Dd(3) was complaining about an itchy bum six weeks ago, so I gave her the tablet and took one myself, washed the sheets/towels etc. She stays a lot with her father, so I asked him to do the same. I even offered him the leftover dose in the packet. Oh no, he wouldn't accept that this could possibly be the case. Any uncleanness was clearly my fault etc etc. And cue one worm life-cycle, here we go again.

If DD is with OP ex a lot of the time, the likelihood is that he has threadworms too and will just pass them back to DD. They are incredibly common and statistics show that around 30% of children are infected at any one time, if I remember correctly.

I think OP was offering the tablet for her ex to take himself and not the second dose for DD. It is standard practice to treat the whole family whether they have symptoms or not as the worms are so highly contagious.